The radiant ceiling of the floor of a 1.5 story makes me shudder a bit. Hopefully there is plenty of air sealing and insulation behind the walls and ceiling of that place or that's a pile of heat getting ejected. I prefer my own heating/cooling not be directly facing or touching a surface where the opposite side is outside the building envelope, the delta T is high enough already.
..personal rant aside. I like these ECM circulators. By the way, the Flat Plate Select link requires a login.
I'm still trying to figure out why the argument for air vs. water always turns to pictures of flex duct and giant chunks of cut out floor joists. If a house has a basement, the ductwork can be installed below the floor joists, that's how ductwork is installed in my house. This also allows for plumbing to be run in the same plane so no penetrations to the floor joists are needed. ..although apparently the electrical contractor opted to drill for the romex. There is no need for large ductwork, a 40k BTUhr 1.5 ton setup would need 600 CFM. Run a trunk box in 4 directions with a decent design using short runs because you don't need to blow air past good windows used in an energy efficient house, only energy inefficient windows. I think the real question is why would you do this anyway, the natural gas connection fee will cost more than the electricity used by air source mini-split heat pumps and a heat pump water heater. ..if the hot water usage is low and you've got low flow heads(1.5 or less gpm such as Niagara Earth) an instant on-demand electric system might even fit the bill without the high initial cost of a HP hot water tank.
It seems to me that hydronic design and implementation is still heavy on labor, in the case of in-floor, ceiling, or other 'wind it all over the house' systems you've got a needlessly complicated system for a house that barely needs heat. A house with a 10,000BTUhr heat load shouldn't need this, your feet won't feel consistently warmer outside of design conditions(and maybe even in design conditions) because if they were, you'd have so much heat coming from the floor that you'd be turning the thermostat down or boiling yourself out.
I think simplicity should be the name of the game. Say you've got a 2000 sq ft foot house with 5BTUhr/sq ft, which is 10,000 BTUhr. You've got 3 bedrooms in close proximity on one side of the house and a living room on another, you could have two 9k mini-splits and that would be oversized. If you really want tight control of the temperature, you could go with 4 zones but I'm thinking this is overkill.
As a personal aside, I've got my house with manual J calcs after I complete my insulation/air seal retrofit down to 10k for 2100 sq ft. If I keep natural gas, I'm going to replace the water heater with a power vent condensing unit and then take the existing HVAC system and plumb a hydronic water coil into it sized to pull no more than 20k BTUhr from the water tank. Thermostat kicks on and the pump from the water tank and the blower kick on. Not too efficient electrically but it won't need to run much and the cost to implement is very low. Most likely I'll be ditching the natural gas though, they keep raising the fixed fee. If I remember right, they are pushing the public utilities commission for $15/month. $180 will be more than the amount I'd spend on heating water and air electrically post retrofit. I'd miss the gas stove, but not that much.
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